Method and system for measuring flow at patient utilizing differential force sensor

ABSTRACT

A fluid delivery system and method for measuring flow at a patient utilizing a differential force sensor in order to precisely control the flow of fluid at very low flow rates. The system includes a fluid line through which a fluid is conveyed to the patient, and a flow controller that selectively varies a rate of flow of the fluid through the fluid line. The differential force sensor can be mounted very close to a point of entry of the fluid into the patient&#39;s body. An onboard communications device is controllably coupled to the flow controller and to the force sensor, responds to an output signal, and provides a feedback to the flow controller in a closed-loop process. The system can pump the fluid at a higher frequency until the flow rate is actually reached at the patient and then adjust to the flow rate needed to ensure patient health.

This application is a continuation of U.S. patent application Ser. No.12/364,270, filed Feb. 20, 2009, and entitled “METHOD AND SYSTEM FORMEASURING FLOW AT PATIENT UTILIZING DIFFERENTIAL FORCE SENSOR”, whichclaims the benefit of U.S. Provisional Patent Application Ser. No.61/140,295, entitled “METHOD AND SYSTEM FOR MEASURING FLOW AT PATIENTUTILIZING DIFFERENTIAL FORCE SENSOR,” filed on Dec. 23, 2008, which areincorporated herein by reference.

TECHNICAL FIELD

Embodiments are generally related to sensor methods and systems.Embodiments are also related to differential force sensors. Embodimentsadditionally relate to differential force sensors utilized in thecontext of monitoring manual patient injections through a fluid line.

BACKGROUND OF THE INVENTION

A variety of fluid delivery systems have been utilized in the medicalfield for delivering fluids (e.g., medication, nutrition, saline, etc)to a patient at relatively precise delivery rates. Such fluid deliverysystems include various types of infusion pumps to administer medicinalfluids automatically and over extended periods of time. A typicalinfusion pump delivers the medicinal fluid into a patient's venoussystem utilizing a delivery channel, which usually includes the use ofan administration tube (e.g., a polyvinyl chloride tube, etc.) connectedto the patient utilizing some form of a catheter, needle, or the like.

For safety reasons and in order to achieve optimal results, it isdesirable to administer the medicinal fluids such as, for example,intravenous (IV) fluids, intermittently and with a frequency as often asmultiple times per day and in a controlled manner as prescribed by thephysician. Depending on the frequency of administration, the patient iseither repeatedly connected to and disconnected from an IV line or iscontinuously connected to an IV line between administrations. In eithercase, the intermittent medications are generally administered by trainedpersonnel utilizing predefined procedures that often include a series ofmanual steps and a large number of disposable supplies. Each manual stepin such procedures increases the risks associated with multiplemanipulations and entry of IV sites.

Accordingly, it will be apparent that it would be desirable to provide arelatively low cost, low complexity system for the delivery of medicinalfluids. A closed-loop system in which a desired parameter is measured tocontrol the system can provide the required accuracy. For example, in aclosed-loop system, it would be preferable to measure flow with a sensorand to control an inexpensive fluid delivery pump based upon themeasured flow rate so as to achieve a desired flow rate. The problemassociated with such disposable deliverable systems for fluids, however,is that such a systems possesses too much compliance to accuratelymeasure the dynamic flow at very low flow rates. Furthermore, theutilized sensor must be sterilized after use or disposed, which is verycostly.

The majority of prior art systems utilize inferred flow measurements atthe infusion pump. However, at low flow rates (e.g., ˜0.05 ml/hr) thetime for the system to overcome the compliance in the disposable tubing(e.g., which can be ˜6-10 feet long) can be measured in hours,particularly in the case of a neo-natal patient where the catheter inthe patient is an extremely small diameter tube and acts as a flowrestrictor. While such systems reflect improvements in the art, they donot control fluid delivery in view of actual flow rates and the timerequired for the fluid to enter the patient increases. In somecircumstances, therefore, such systems may require time ability todeliver fluids over a wide range of delivery rates including very lowflow rates. Moreover, conventional manufacturing techniques tend to beexpensive and, therefore, are not well suited for use in manufacturingdisposable items.

Based on the foregoing, it is believed that a need exists for animproved differential force sensor for monitoring manual injectionsthrough the fluid line. A need also exists for an improved fluiddelivery system for precisely controlling the flow of the fluid into thepatient at very low flow rates and to minimize system compliance.

BRIEF SUMMARY

The following summary is provided to facilitate an understanding of someof the innovative features unique to the embodiments disclosed and isnot intended to be a full description. A full appreciation of thevarious aspects of the embodiments can be gained by taking the entirespecification, claims, drawings, and abstract as a whole.

It is, therefore, one aspect of the present invention to provide for animproved differential force sensor apparatus capable of automaticallymonitoring manual injections through a fluid line.

It is another aspect of the present invention to provide for an improvedfluid delivery system for precisely controlling the flow of the fluidinto the patient at very low flow rates and to minimize systemcompliance.

The aforementioned aspects and other objectives and advantages can nowbe achieved as described herein. A fluid delivery system and method formeasuring flow at a patient utilizing a differential force sensor inorder to precisely control the flow of fluid into a patient at very lowflow rates is disclosed. The system includes a fluid line through whicha medicinal fluid is conveyed from a reservoir to the patient. A flowcontroller is also provided, which can be employed to selectively vary arate of flow of the medicinal fluid through the fluid line. Thedifferential force sensor can be mounted on the patient and very closeto a point of entry of the fluid into the patient's body. An onboardcommunications device can be controllably coupled to the flow controllerand to the differential force sensor that monitors a rate of flow of themedicinal fluid through the fluid line, thereby producing an outputsignal that is indicative of flow rate and/or other data. The onboardcommunications device responds to the output signal(s), is capable ofproviding feedback to the flow controller in a closed-loop process, andis able to achieve the desired rate of infusion of the medicinal fluidinto the patient. The system can pump the fluid at a higher frequencyuntil the flow rate is actually attained at the patient and thenadjusted to the flow rate required to ensure patient health.

The differential force sensor includes the use of two piezoresistivesense die packaged in close proximity to one another. The differentialforce sensor and components such as the two (or more) piezoresistivesense die can be packaged utilizing any number of packaging processes.The two piezoresistive sense die configuration can be utilized tomeasure force exerted on a diaphragm on either side of an orifice. Thepiezoresistive sense die can be packaged in close proximity to makeintimate contact with a diaphragm(s) located on either side of theorifice.

The differential force sensor further includes one or more plungers thatare capable of making intimate contact with the diaphragm andtransferring the force to the piezoresistive sense die. The differentialforce sensor can be mounted very close to the point of entry into thepatient's body. Such differential force sensor is capable of monitoringmanual injections through the fluid line. The output of the sensor canbe the individual force measurements in the form of an electrical signal(either digital or analog) and potentially a differential signal (thedifference between the two sense elements). Additionally, one or moreASIC components and microcontrollers can be utilized to provide thermalcalibration and differential calculation.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, in which like reference numerals refer toidentical or functionally-similar elements throughout the separate viewsand which are incorporated in and form a part of the specification,further illustrate the embodiments and, together with the detaileddescription, serve to explain the embodiments disclosed herein.

FIG. 1 illustrates a block diagram of a fluid delivery system comprisinga differential force sensor, in accordance with a preferred embodiment;

FIG. 2 illustrates a cross-sectional view of the differential forcesensor of FIG. 1, in accordance with an alternative embodiment;

FIG. 3 illustrates a schematic diagram of an intravenous fluid deliverysystem utilizing the differential force sensor of FIGS. 1-2 on eitherside of an orifice for monitoring manual injections, in accordance withan alternative embodiment; and

FIG. 4 illustrates a high level flow chart of operations illustratinglogical operational steps of a method for measuring flow at a patientutilizing the differential force sensor of FIGS. 1-3, in accordance withan alternative embodiment.

DETAILED DESCRIPTION

The particular values and configurations discussed in these non-limitingexamples can be varied and are cited merely to illustrate at least oneembodiment and are not intended to limit the scope thereof

FIG. 1 illustrates a block diagram of a fluid delivery system 100 thatincludes a differential force sensor 200, in accordance with a preferredembodiment. The fluid delivery system 100 includes a fluid supply 110 ofany desired parenteral fluid and a pump 120, which may be, for example,a peristaltic pump, to which is connected to a tube 125, which in turnis connected to a cannula inserted into the vein of a patient 155. Notethat the embodiments discussed herein should not be construed in anylimited sense. It can be appreciated that such embodiments revealdetails of the structure of a preferred form necessary for a betterunderstanding of the invention and may be subject to change by skilledpersons within the scope of the invention without departing from theconcept thereof

The pressure in the tube 125 can be monitored by the differential forcesensor 200, which can be connected to an ASIC 330 for supplying digitaldata representing the pressure in the tube to a microcontroller 320.Note that some embodiments can utilize one ASIC per sense die and thusutilize two ASIC's capable of communicating the microcontroller 320. Thedifferential force sensor 200 is also capable of monitoring manualinjections through the fluid line. The output of the sensor 200 can bethe individual force measurements in the form of an electrical signaleither digital or analog and potentially a differential signal (i.e.,the difference between the two sense elements 240). The ASIC 330 can beutilized to provide linearization and thermal compensation through theimplementation of calibration and differential calculation operations.The microcontroller 320 can be utilized to provide a differentialcalculation or a flow rate calculation and also to communicate withexternal electronics through an onboard communications device 340.

The microcontroller 320 can be provided as a single integrated circuitchip that contains a processor (e.g., CPU), a non-volatile memory forthe program (e.g., ROM or flash), volatile memory for input and output(e.g., RAM), a clock, and an I/O control unit. Microcontroller 320 canthus function as a “computer on a chip”.

Note that the term “ASIC” as utilized herein is an acronym forApplication Specific Integrated Circuit. ASIC 330 can thus be providedin the form of an integrated circuit chip that is custom designed for aspecific application rather than a general-purpose chip such as amicroprocessor. ASICs generally improve performance over general-purposeCPUs because ASICs are capable of being “hardwired” to perform aspecific job and do not incur the overhead of fetching and interpretingstored instructions. In some embodiments, however, a standard cell ASICmay include one or more microprocessor cores and embedded software, inwhich case, it may be referred to as a “system on a chip” (SoC). Thus,the ASIC 330 discussed herein may constitute in an alternativeembodiment, an SOC.

The microcontroller 320 generally provides one or more output signals toa flow rate controller 140, which controls the rate of flow delivered bythe pump 120 through the onboard communications device 340. In someembodiments, the microcontroller 320 can also communicate electronicallywith an operator display 180 and can generate an alarm signal 190through the onboard communications device 340. The microcontroller 320can also be enabled to accept operator input 160 for controlling therate of flow and the like. In a preferred embodiment, however, themicrocontroller 320 communicates with an external device, such as anexternal operator display 180. In other words, microcontroller 320 candrive external devices, such as display 180. While a microcontroller 320could be packaged with a display such as display 180 or an alarm such asalarm 190, this would not be practical, because such devices would thenhang from the patient's arm or leg. The preferred implementationinvolves the use of such external devices driven by microcontroller 320.

The differential force sensor 200 can be mounted on the patient and veryclose to the point of entry into the body for sensing a differentialflow of the fluid in the tube 125 and for generating a flow rate signalindicative of a rate of flow of the fluid in the tube 125. The flow ratecontroller 140 selectively varies a rate of flow of the medicinal fluidthrough the fluid line. The flow rate controller 140 controls the pump120 and causes adjustments to the output rate of the pump 120 as afunction of the flow rate signal, whereby the desired flow rate issubstantially achieved. The onboard communications device 340 can becontrollably coupled to the flow controller 140 and to the differentialforce sensor 200 that monitors the rate of flow of the medicinal fluidthrough the fluid line, thereby producing an output signal indicative ofthe rate of fluid flow.

The onboard communications device 340 can respond to the output signaland generate a feedback signal to the flow controller 140 in aclosed-loop process, in order to thereby achieve a desired rate ofinfusion of medicinal fluid into the patient. Note that the onboardcommunications device 340 may constitute, for example, a USB portcapable of communication via any communication protocol and/or othertypes of high-speed communication devices, depending upon designconsiderations. Also note that the term “medicinal fluid” as utilizedherein can refer to medication, nutrition, saline and/or any other fluidnecessary for the health and well-being of a patient receiving suchfluid.

FIG. 2 illustrates a cross-sectional view of the differential forcesensor 200 of FIG. 1, modified to include two piezoresistive sense die240 each glued to the PCB 260, in accordance with an alternativeembodiment. Note that in FIGS. 1-2, identical or similar parts orelements are generally indicated by identical reference numerals. Thedifferential force sensor 200 depicted in FIG. 1 can be configured toinclude two piezoresistive sense die 240 that are packaged in closeproximity to one another and glued to a PCB (Printed Circuit Board) 260.A molded housing 225 can be positioned over the sense die 240 and thegel 220 dispensed and cured into the orifice 410 (i.e., not shown inFIG. 2, but depicted in FIG. 3) above the sense die 240 so it makesintimate contact with the topside of the sense die 240.

A diaphragm 215 and a plunger 245 can be placed on top of the gel 220.The two piezoresistive sense die 240 can be utilized to measure forcesexerted on the diaphragm 215 on either side of the orifice 410. Theforces F1 and F2 from the diaphragm 215 can be transmitted through theplungers 245 and into the gel 220 and finally into the piezoresistivesense die 240. The signal compensation for the piezoresistive sense die240 can be completed through the ASICs 330. The microcontroller 320 canbe utilized to communicate with external electronics through the USBcable 340. The differential force sensor 300 can be covered with abottom cover 350 and a top cover 360.

Note that the embodiments discussed herein should not be construed inany limited sense. It can be appreciated, of course, that other types ofpackaging processes may also be utilized such as, for example, the sensedie glued to the PCB, wherein as a ball bearing makes intimate contactwith the sense die diaphragm, the force is transmitted to the ballbearing, and so forth. However, it will be apparent to those skilled inthe art that other packaging processes can be utilized as desiredwithout departing from the scope of the invention.

Such differential force sensor 200 is a high-performance transducerspecifically designed to address the needs of medical and specializedOEM (Original Equipment Manufacturer) applications. The differentialforce sensor 200 can be specified to operate with either a constantcurrent or voltage supply. The differential force sensor 300 employs asolid state piezoresistive pressure transducer mounted in a plasticpackage. Such an approach provides a reliable solution for applicationswhere force can be applied by a flexible membrane to the sensor, such asfound in infusion pumps. The differential force sensor 200 is alsocapable of providing access to important safety features in criticalcare medical instrumentation, such as occlusion detection orinfiltration detection. The pressure data can provide medical personnelwith useful diagnostic information regarding the condition of thepatient's circulatory system. The differential force sensor 200 can alsobe utilized with other medical dispensing devices, such as syringepumps, to improve safety and accuracy.

FIG. 3 illustrates a schematic diagram of an intravenous fluid deliverysystem 300 capable of utilizing the differential force sensor 200 shownin FIGS. 1-2 on either side of the orifice 410 for monitoring manualinjections, in accordance with an alternative embodiment. Note that inFIGS. 1-3, identical or similar parts or elements are generallyindicated by identical reference numerals. The intravenous fluiddelivery system 300 depicted in FIG. 3 can be configured to include anintravenous tube 420 and an injection point 430 for deliveringmedications to a patient, as illustrated by arrow 450. The differentialforce sensor 200, which includes piezoresistive sense die 240, can beplaced on either side of the orifice 410 for measuring differentialforce on either side of the orifice 410. The piezoresistive sense die240 can be utilized to measure forces F1 and F2 exerted on the diaphragm215 on either side of the orifice 410. The piezoresistive sense die 240can be packaged in close proximity to make intimate contact with thediaphragm(s) 215 located on either side of the orifice 410.

Intravenous medications such as, for example, antibiotics, antivirals,antiemetics, chemotherapy, and biotechnology drugs can be administratedintermittently with a frequency through the injection point 430. Thedifferential force sensor 200 can be mounted very close to the point ofentry into the patient's body. The differential force sensor 200 iscapable of monitoring manual injections through the intravenous line420. Such small size and lightweight differential force sensor formonitoring manual injections through the intravenous line 420 reducepatient discomfort.

For example, in delivering medicine to a baby in a critical careenvironment, the amount of medicine to be delivered is prescribed by thedoctor and the medical staff worker gets the medicine into the patient.The sensor 200 can be mounted on the baby very close to the point ofentry into the body; hence, the system 300 is capable of avoiding all ofthe compliance right up to the baby's catheter and the medicine can beinto the patient within 10′s of minutes, instead of hours. The time fromprescription to implementation can also be minimized. Another factor toconsider is the concentration of medicine. In some instances, a doctormay prescribe a high concentrated medicine that flows into the patientat very low flow rates and causes the same problem. The system andmethod disclosed herein can at least ensure that at the system start,fluid is flowing into the patient at the prescribed rate.

FIG. 4 illustrates a high level flow chart of operations illustratinglogical operational steps of a method 400 for measuring flow at apatient utilizing the differential force sensor 200, in accordance withan alternative embodiment. Again as reminder, in FIGS. 1-4, identical orsimilar parts or elements are generally indicated by identical referencenumerals. FIG. 4 thus illustrates a variation to the previously depicteddrawings of FIG. 1-3. The differential force sensor 200 can be mountedon the patient and very close to the point of entry into the body inorder to read the flow closer to the patient, as depicted at block 410.The amplified flow rate signal indicative of a rate of flow of fluid canbe generated, as depicted at block 420. The amplified signals from thedifferential force sensor 200 can be fed to the onboard communicationsdevice 340, as depicted at block 430. Thereafter, as illustrated atblock 440, feedback can be provided to the flow controller 140 throughthe communication channel associated with the communication device 340.The communication channel is open to the fluid delivery system 100 andprovides feedback to allow for closed loop control of the fluid flowinto the patient. The flow of medicinal fluid into the patient can becontrolled at very low flow rates and time required for the fluid toenter the patient can be minimized, as shown at block 450. Note that themethod 400 described herein also can be configured for closed loopcontrol of the fluid flow into the patient.

The differential force sensor 200 can be mounted on the patient veryclose to the point of entry into the body and allows for a fluiddelivery system to read the flow closer to the patient and take out orminimize the compliance of all elements up to the patient's catheter.The placement of the differential force sensor 200 allows the fluiddelivery system 100 to pump the fluid at a higher frequency until theflow rate is actually reached at the patient and then adjusts to theflow rate needed to ensure patient health. It is believed that byutilizing the system and approach described herein, the delivery systemcan precisely control the flow of the fluid into the patient at very lowflow rates and minimizes the time required for the fluid to enter thepatient. Note that in some embodiments the disclosed differential flowsensor can be implemented as a disposable pressure sensor.

It will be appreciated that variations of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be desirablycombined into many other different systems or applications. Also, thatvarious presently unforeseen or unanticipated alternatives,modifications, variations or improvements therein may be subsequentlymade by those skilled in the art which are also intended to beencompassed by the following claims.

1. A system for controlling fluid flow that is delivered through a fluidline that enters a patient, the system comprising: a reducedcross-section orifice situated adjacent a point of entry of a fluid lineinto said patient; a differential force sensor including: a first forcesensor; a second force sensor positioned adjacent the first forcesensor; wherein said first force sensor is responsive to movement of afirst flow diaphragm that is exposed to a first pressure in said fluidline upstream of the reduced cross-section orifice, and said secondforce sensor is responsive to movement of a second flow diaphragm thatis exposed to a second pressure in the fluid line downstream of thereduced cross-section orifice; a first plunger associated with the firstforce sensor, wherein a first force exerted by movement of said firstflow diaphragm in response to said first pressure is transferred to saidfirst force sensor through said first plunger; a second plungerassociated with the second force sensor, wherein a second force exertedby movement of said second flow diaphragm in response to said secondpressure is transferred to said second force sensor through said secondplunger; and said first force sensor and said second force sensorproviding one or more sensor output signals; a flow controller thatcontrols a rate of flow of said fluid through said fluid line; and oneor more electronic devices, the one or more electronic devicesresponding to said one or more sensor output signals of said first forcesensor and said second force sensor and providing one or more feedbacksignals to said flow controller, in a closed-loop manner, such that theflow controller actively controls the rate of flow of said fluid throughsaid fluid line and into said patient.
 2. The system of claim 1, whereinsaid one or more electronic devices are configured to perform signalprocessing on said one or more sensor output signals, wherein saidsignal processing includes performing a thermal compensation and/or adifferential pressure calculation.
 3. The system of claim 1, whereinsaid fluid comprises a medicinal fluid.
 4. A system for controllingfluid flow that is delivered through a fluid line, comprising: a reducedcross-section orifice situated along the length of said fluid line; afirst sense die and a second sense die positioned adjacent to oneanother, wherein said first sense die is responsive to movement of afirst flow diaphragm that is exposed to a first pressure in said fluidline upstream of the reduced cross-section orifice, and said secondsense die is responsive to movement of a second flow diaphragm that isexposed to a second pressure in the fluid line downstream of the reducedcross-section orifice, said first sense die and said second sense dieproviding one or more sensor output signals; a flow controller thatcontrols a rate of flow of said fluid through said fluid line; and oneor more electronic devices, the one or more electronic devicesresponding to said one or more sensor output signals of said first sensedie and said second sense die and providing one or more feedback signalsto said flow controller, in a closed-loop manner, such that said flowcontroller actively controls the rate of flow of said fluid through saidfluid line.
 5. The system of claim 4, wherein said reduced cross-sectionorifice situated adjacent a downstream end of said fluid line, and saiddownstream end of said fluid line is positioned within a patient, suchthat said reduced cross-section orifice is situated proximate a point ofentry of said fluid line into said patient.
 6. The system of claim 5,wherein said fluid comprises a medicinal fluid.
 7. The system of claim5, wherein said fluid comprises saline.
 8. The system of claim 5,wherein said fluid comprises a nutritional fluid.
 9. The system of claim4, wherein said fluid controller causes the fluid flow to be initiallyconveyed at a higher rate of fluid flow until the fluid arrives adjacentto said reduced cross-section orifice, and then said fluid controllercauses the fluid flow to be adjusted as needed to provide a desiredlower rate of fluid flow through said fluid line.
 10. The system ofclaim 4, wherein said one or more electronic devices are configured toperforming signal processing on said one or more sensor output signals,wherein said signal processing includes performing a thermalcompensation and/or a differential pressure calculation.
 11. The systemof claim 4, wherein said first sense die and said second sense die arehoused in a common sensor package.
 12. The system of claim 4, whereinsaid first sense die, said second sense die, and said one or moreelectronic devices are housed in a common sensor package.
 13. The systemof claim 4, further comprising: a first plunger associated with thefirst sense die, wherein a first force exerted by movement of said firstflow diaphragm in response to said first pressure is transferred to saidfirst sense die through said first plunger; and a second plungerassociated with the second sense die, wherein a second force exerted bymovement of said second flow diaphragm in response to said secondpressure is transferred to said second sense die through said secondplunger.
 14. The system of claim 4, wherein: each of the first sense dieand said second sense die is fixed relative to a printed circuit board;a housing is located over said first sense die and said second sensedie; a first sensor orifice positioned directly adjacent said firstsense die; a second sensor orifice positioned directly adjacent saidsecond sense die; and a gel situated in said first sensor orifice andsaid second sensor orifice.
 15. The system of claim 14, furthercomprising: a first plunger associated with the first sense die, whereina first force exerted by movement of said first flow diaphragm istransferred to said first sense die through said first plunger and saidgel in said first sensor orifice; and a second plunger associated withthe second sense die, wherein a second force exerted by movement of saidsecond flow diaphragm is transferred to said second sense die throughsaid second plunger and said gel in said second sensor orifice.
 16. Amethod for delivering a fluid into a patient, said method comprising:providing a fluid line and a flow controller, wherein the fluid lineincludes a reduced cross-section orifice situated adjacent a point ofentry of the fluid line into said patient; providing a differentialforce sensor having a first force sensor and a second force sensorpositioned adjacent to one another, wherein said first force sensor isresponsive to movement of a first flow diaphragm that is exposed to afirst pressure in said fluid line upstream of the reduced cross-sectionorifice, and said second force sensor is responsive to movement of asecond flow diaphragm that is exposed to a second pressure in the fluidline downstream of the reduced cross-section orifice, said differentialforce sensor providing a measure of a flow rate of the fluid through thefluid line; providing a feedback signal to the flow controller, whereinthe feedback signal is related to the measure of the flow rate of thefluid provided by the differential force sensor; and conveying saidfluid from a reservoir to said patient through said fluid line, whereinsaid flow controller uses the feedback signal in a closed loop manner toactively control the flow rate of the fluid through said fluid line. 17.The method of claim 16 wherein said fluid includes a medicinal fluid.18. The method of claim 16 wherein said fluid includes saline.
 19. Themethod of claim 16 wherein said fluid includes a nutritional fluid. 20.The method of claim 16 further comprising initially conveying said fluidat a higher flow rate until the fluid arrives adjacent the point ofentry of the fluid into the patient, wherein said flow rate isthereafter adjusted as needed to provide a lower desired flow rate ofsaid fluid into said patient.